WM9708

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 April 2001

12

AC-LINK DIGITAL SERIAL INTERFACE PROTOCOL

The WM9708 incorporates a 5-pin digital serial interface that links it to the AC’97 controller. The AC-

link is a bi-directional, fixed rate, serial PCM digital stream. It handles multiple input and output audio

streams, as well as control Register accesses, employing a time division multiplexed (TDM) scheme.

The AC-link architecture divides each audio frame into 12 outgoing and 12 incoming data streams,

each with 20-bit sample resolution and a 16-bit header slot. With a minimum required DAC and ADC

resolution of 16-bits, AC’97 may also be implemented with 18 or 20-bit DAC/ADC resolution, given

the headroom that the AC-link architecture provides. The WM9708 provides support for 18-bit

operation.

SLOT

NUMBER

SYNC

SDATAOUT

SDATAIN

TAG PHASE

TAG

CMD

ADR

CMD

DATA

PCM

LEFT

PCM

RIGHT

RSRVD

RSRVD

RSRVD

TAG

STATUS

ADDR

STATUS

DATA

PCM

LEFT

PCM

RIGHT

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

DATA PHASE

01

2

3

4567

89

10

11

12

PCM C

(n+1)

PCM R

(n+1)

PCM L

(n+1)

CODEC ID

SLOTREQ 3-12

PCM

CENTRE

RSRVD

PCM

L SURR

PCM

R SURR

PCM

LFE

RSRVD

Figure 8 AC’97 Standard Bi-directional Audio Frame

SYNC

BITCLK

SDATAOUT

VALID

FRAME

SLOT(1)

SLOT(2)

SLOT(12)

’0’

(ID1)

(ID0)

19

0

19

0

19

0

19

0

TAG PHASE

DATA PHASE

20.8

µS (48kHz)

12.288MHz

81.4nS

END OF PREVIOUS

AUDIO FRAME

TIME SLOT ’VALID’ BITS

(’1’ = TIME SLOT CONTAINS

VALID PCM DATA)

SLOT (1)

SLOT (2)

SLOT (3)

SLOT (12)

Figure 9 AC-link Audio Output Frame